Proposed studies attempt to isolate, purify and determine the structure of bovine pineal antigonadotropin. Biologically active substances are extracted from bovine pineal glands and purified using Sephadex gel filtration, Amicon ultrafiltration, ion exchange chromatography, paper chromatography and electrophoresis, and high performance liquid chromatography preparatory to structure determination by mass spectrometry. Biological tests for active principals include inhibition of compensatory ovarian hypertrophy, blockage of ovulation, retardation of puberty and reduction of serum LH and prolactin in rats and mice. The pineal antigonadotropic peptide Thr-Ser-Lys has been synthesized and is one principle being tested. Other experiments are aimed at the identification of the site(s) and mechanism(s) of action of pineal antigonadotropic substances. Additionally, pineal secretion of antigonadotropic substances is studied in vitro using rat pineal glands and electron microscopy is employed to study pinealocyte dense cored vesicles which may represent a major secretory product.